Japanese Patent Publication 56-30124 discloses a system for detecting abnormal phenomenon between electrodes in an electrolytic finishing system where an electrode is moved to maintain a small gap formed between the electrode and the work. In the system, a spark generating between the electrode and the work is detected. Japanese Patent Publication 57-22690 discloses a system for predicting a short circuit in an electrolytic finishing process where a work is subjected to the electrolytic finishing process by supplying a pulse current to a wire which serves as an electrode.
In the former abnormality detecting system, a decrease of voltage and an increase of current magnitudes of which is caused by a spark are detected. However, the generation of the spark is an abnormal phenomenon itself, and hence the work would have been burnt by the spark. Therefore, in an electrolytic finishing method disclosed in Japanese Patent Application Laid-Open 63-216628 where the work is electrolytically finished, using an electrode having a surface corresponding to a machining surface of the work, there is a critical problem that the work machined to a desired three-dimensional shape is burnt in a second.
The latter short circuit detecting method detects the occurrence of the short circuit, and not the abnormal phenomenon. A discharge voltage, while the supply of the machining pulse is stopped, is detected. The detected voltage, which substantially is constant during normal operation, abnormally decreases from the detected discharge voltage when the short circuit is expected. Therefore, the short circuit can be detected by the abnormal decrease of the discharge voltage. However, it is not possible to predict the short circuit while the machining pulse is being supplied. In the electrolytic machining method described above, when the pulse width of the machining pulses is relatively large, a short circuit occurs due to residual products formed in the gap while the machining pulse is fed, which causes a burn of the work.
The object of the present invention is to provide a method for solving the above described problems, wherein an occurrence of an arc is predicted, while a machining pulse is applied, so as to prevent the short circuit beforehand, thereby preventing the work from burning.